Currently, high-level support (using username: password @ in URLs) for authorization is not implemented in the HTTP Rebol 3 scheme.
However, you can easily send the HTTP Authorization header directly (for HTTP "basic" auth):
read [ scheme: 'https host: "mail.google.com" path: "/mail/feed/atom" headers: [Authorization: join "Basic " enbase/base "user:pass" 64] ]
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